This invention relates to hydraulic torque wrenches used for rotating mechanical components, for example for tightening or loosening nuts, bolts and screws, and more particularly to wrenches capable of providing a substantially constant torque and of maintaining such a torque over a relatively long stroke of the associated piston.
Our published European specification no. 0382408 discloses a constant torque wrench of this type which includes a body member incorporating a hydraulic piston-cylinder assembly, and a housing incorporating a ratchet drive mechanism. The drive mechanism includes a pivotal drive lever provided with a cylindrical neck portion remote from the pivot axis of the lever, said neck portion being slidably received within the cylindrical bore of a spherical bearing member linearly movable with the piston of the piston-cylinder assembly.
The provision of the spherical bearing member, which is preferably housed within a cylindrical shuttle member secured to, to be movable with, the piston, enables the linear movement of the piston to be translated into angular movement of the drive lever in a manner which achieves substantially constant torque throughout the length of the piston stroke, while at the same time the spherical nature of the bearing member, and the associated substantially universal movement it can undergo, accommodates the torsional and bending forces transmitted through the body member during normal operation.
The above-described tool is particularly suited to dual purpose use for both conventional and limited access situations.
For conventional use, a housing accommodating a square drive is provided to which can be attached a variety of different sockets.
For limited access use, the housing with the square drive is replaced by a low profile housing incorporating a socket of the desired dimensions.
Thus it will be appreciated that the housings should be easily interchangeable such that the exchange can be made without the need for specialised tooling, holding devices and the like.
Although removal of a housing from a body member is readily achieved and attachment of a housing to a body member can be achieved relatively easily with care and experience, situations have arisen whereby care has not been exercised and damage has occurred.
Prior to assembly, it is necessary to locate the spherical bearing member in a position whereby the bore therethrough is positioned to receive therein the neck portion of the drive lever as the housing is mounted on the body member. In view of the substantially universal movement the bearing member can undergo, it is possible for the bore therein to be inadvertently or accidently misaligned with the neck portion of the drive lever whereby assembly cannot be completed until the bearing member is realigned. This problem is exacerbated if, as is preferable, the neck portion of the drive lever is a close sliding fit in the bore through the bearing member.